In bicycle suspension design, emphasis is most frequently placed on the stability and equilibrium of the cyclist. Most designs aiming at this objective therefore create suspensions that are “plush” or soft, so that the suspension is responsive to uneven terrain over which the bicycle is pedalled. Suspension designs have also aimed at increasing the degree of suspension travel, that is, the extent of displacement available for the wheel relative to the frame.
However, it is recognised that softer suspension characteristics and/or high suspension travel designs have a drawback. When a cyclist is pedalling, all of the human pedalling energy dissipated in pedalling should ideally be transmitted to the rear wheel of the cycle. In practice, some energy is lost in the conversion of pedal rotation through the chain to the rear wheel. Where soft suspensions are placed adjacent in the rear wheel, it is common for the suspension to compress under the pedalling energy, thus robbing even more pedalling energy. The compression and expansion of the soft suspension, and the resulting motion of the rear wheel in rhythm with the pedalling motion is commonly known as “pedal-induced bobbing”.
U.S. Pat. No. 6,131,934 to Sinclair describes a bicycle rear suspension employing two shock absorbers. The Sinclair design is directed especially for downhill racing bicycles where the rear suspensions are subjected to large impact forces that may cause the rear suspension to “bottom out”. On the other hand, a stiffer rear suspension can handle large impact forces, but loses the ability to tract smaller “stutter” lumps. To address this, Sinclair uses two spring and damper assemblies, where a soft primary spring and damper assembly is designed to absorb most impacts and a stiffer secondary spring and damper assembly comes into effect to handle larger impacts. Because there is no provision make to prevent the spring and damper assemblies from compressing under pedalling force, the Sinclair design is also susceptible to pedal-induced bobbing.
I have designed a two-stage suspension arrangement using two suspension elements, such as shock absorbers, that can provide maximum suspension travel when the cyclist is not pedalling and to provide minimum suspension travel when pedalling forces are applied. This allows the suspension assembly to absorb impact forces efficiently while not suffering the extent of pedal-induced bobbing of common suspension design.
Accordingly, it is an object of this invention to go some way to achieving this desideratum or to at least provide the public with an effective alternative.